1. Field of the Invention
The invention relates to a recording apparatus, in particular, to a heat transfer recording apparatus using an ink film wherein characters and/or graphic images are formed on recording paper of various widths.
2. Description of the Related Art
A heat transfer recording apparatus such as a printer comprises a platen roller and a thermal head that can be arbitrarily pressed against the platen roller. The recording paper is transferred together with the ink film between the platen roller and the thermal head to allow characters and/or graphic images printed thereon. The ink film has thermally fusing or sublimating type of inks coated on one side thereof. The ink is fused or sublimated to be fixed on the recording paper by means of the heat of the thermal head.
A heat transfer recording apparatus is normally capable of printing onto various sizes of recording paper. For example, recording paper larger than A4 in addition to paper of sizes as small as A6 paper, post card, card-size paper can be optionally applied to the recording apparatus.
However, a problem has been noticed of such an apparatus that, after having been used for some time, the printing density becomes uneven across the width of the paper depending on how often the apparatus has been used. More specifically, when an image of a uniform density is printed on a wide sheet of recording paper, the printed image becomes darker in the midsection of the paper than on the edges of the width.
It is caused by the fact that the midsection of the platen roller and the thermal head where all sizes of paper pass wear more rapidly than the edges where only larger sizes of paper pass, thus increasing the heat conductivity in the midsection.
This problem can be eliminated by replacing the platen roller and/or thermal head when it is found that the density unevenness develops between the midsections and the edges of the recording paper. However, this method is not recommendable because of the resultant increase of the running cost.